n. (context protein English) A polypeptide hormone that is released by the chief cells of the parathyroid glands and is involved in raising the levels of calcium ions in the blood.
n. hormone synthesized and released into the blood stream by the parathyroid glands; regulates phosphorus and calcium in the body and functions in neuromuscular excitation and blood clotting [syn: parathormone]
'Parathyroid hormone (PTH'), also called parathormone or parathyrin, is secreted by the chief cells of the parathyroid glands as a polypeptide containing 84 amino acids, yet effective hormone-receptor interaction requires solely the 34-N-terminal amino acids. While PTH acts to increase the concentration of ionic calcium (Ca) in the blood, calcitonin, a hormone produced by the parafollicular cells (C cells) of the thyroid gland, acts to decrease ionic calcium concentration. PTH essentially acts to increase the concentration of calcium in the blood by acting upon the parathyroid hormone 1 receptor, which is present at high levels in bone and kidney, and the parathyroid hormone 2 receptor, which is present at high levels in the central nervous system, pancreas, testis, and placenta. PTH half-life is approximately 4 minutes. It has a molecular mass of approximately 9500 Da.